The invention relates to photoelastic sensing means, and more particularly to photoelastic sensing means capable of providing high sensitivity for measuring pressure, force, displacement, acceleration or inertial force, proximity, temperature and other measurands.
Sensing devices and transducers in which the variation of stress in a sensing member provides a corresponding electrical output are known in the art. Such devices include strain gauges, magnetoelastic measuring transducers, piezo-transister measuring transducers, optical measuring transducers, and photoelastic measuring transducers. The deficiences of such prior art devices included providing small output signals, having limited frequency response characteristics for dynamic measurements, having poor signal to noise characteristics, being unable to provide high sensitivity for various ranges of measurements, and being complex and difficult to construct and operate. Thus, the piezo-optic or photoelastic measuring transducer described in U. S. Pat. No. 3,950,987 of Isaak Isaevich Slezinger et al requires a plurality of polarization-optical channels in special arrangements and with phasing means for each channel in order to produce a plurality of output signals which are compared to provide the output information. The requirement for such multiplicity of channels and components increases the complexity and the cost for manufacture and maintenance of the photoelastic transducer. This transducer also does not provide the very high sensitivity desirable for measuring low level pressures and forces applied to the photoelastic sensing means.